It's likely that in ancient biblical texts they based age on lunar years. A lunar year is 28 days +/-, so there are roughly 12 lunar years to a solar year. Therefore Methusala was most likely around 79-80 years old, which is no less of a feat given the time that he lived!

And #6 is a bit misleading. The turritopsis nutricula reverts to a polyp colony and then regrows from there. http://www.huffingtonpost.com/2012/11/29/immortal-jellyfish-lives-forever-reverts-stage-life_n_2207583.html

@MonkeyMonster so you mean to tell me that Enos,grandson of Adam son of Seth was 90 years old when he begat Cainan, so in your "lunar year" equations he was 7 1/2 years old???? Gen 5:9.. no they really lived up to 900 years old, and ALL of this is lies nobody can tell the age of anything,not even by carbon dating or any method out there.